Structural timbers are liable to rot; the rot is caused by fungal infection which is more acute when the timber is wet. One familiar way of preserving timber is to impregnate it with a wood preservative and for this purpose there are used as preservative either creosote or various metal salts in solution.
Another method of preservation is to make a small hole in the timber at an appropriate position and put a solid wood preservative in the hole, so that it will slowly dissolve in water and then be transported to adjacent parts of the timber where it establishes a protected zone. The theory behind the use of inserted solids is that they form a reservoir, so that as the concentration of timber preservative in the `protected zone` falls, by diffusion or leaching of the preservative, more preservative is released.
In the Swedish Journal "Jarnvags-Teknik" No. 1 of 1955 there is described a cartridge for insertion in a cavity formed in timber; this consists of a particulate wood-preservative salt bound together with a binder and contained in a fabric envelope.
It is an object of the present invention to provide a method of establishing a reservoir of wood preservative in timber, such that the time over which the preservative is dissipated into the surrounding zone to protect it from decay is prolonged.
It is a further object of the invention to provide a method of preserving timber in which there is used a novel, long-lasting, wood preservative element.
Another object of this invention is to provide a method of preserving timber in which there is used a source of boric acid more concentrated than boric acid itself.